Arc suppression circuit using a semi-conductor switch

Abstract

An arc suppression circuit in a protection relay having trip contacts is used to turn off a battery-powered solenoid and trip an AC power circuit breaker. The arc suppression circuit uses a switch-control circuit to control the turning off of a semi-conductor switch so that the semi-conductor switch provides a current path around the trip contacts, and is carrying all, or substantially all, of the load current, before the trip contacts are opened. When the trip contacts begin to open, the switch-control circuit holds the semi-conductor switch on for a sufficient time to prevent an arc from becoming established before turning the semi-conductor switch off. In a second embodiment, the arc suppression circuit provides a second switch-control circuit. This second switch-control circuit is configured to accept control signals from a microprocessor within a protection relay. The microprocessor turns the semi-conductor switch on before the contacts begin to open, thereby providing a current path around the contacts before the contacts begin to open. The microprocessor turns the semi-conductor switch off after a time sufficient to prevent an arc from becoming established.

1. An arc suppression circuit for suppression of arcing across trip contacts coupled to operate a battery-powered solenoid, the battery-powered solenoid including a battery and a solenoid, the circuit comprising:
 a semi-conductor switch connected across the battery-powered solenoid; and 
 a switch-control circuit controlling the semi-conductor switch; 
 wherein the switch-control circuit is configured such that while the contacts are closed, the semi-conductor switch is on, providing a current path around the contacts, and when the contacts begin to open, the semi-conductor switch remains on and continues to provide the current path around the contacts for a sufficient time after the contacts begin to open to prevent an arc from becoming established, wherein the semiconductor switch carries substantially all of the current flowing through the battery-powered solenoid when providing the current path around the contacts when the contacts are closed and when the contacts begin to open. 
 
   
   
     2. An arc suppression circuit according to  claim 1 , wherein after the contacts begin to open, the current path around the contacts is maintained for a predefined time that is determined by the time constant of a resistance and a capacitance. 
   
   
     3. An arc suppression circuit according to  claim 2 , wherein the semi-conductor switch is a power transistor having a gate, and wherein the switch-control circuit includes:
 a capacitor connected in series with the contacts and the battery-powered solenoid; and 
 a voltage divider connected across the capacitor, the voltage divider having an output coupled to the gate. 
 
   
   
     4. An arc suppression circuit according to  claim 3 , wherein the power transistor is an insulated gate bipolar junction transistor (IGBT). 
   
   
     5. An arc suppression circuit according to  claim 3 , further comprising a clamping diode coupled to the gate, whereby the power transistor is protected from overvoltage applied at its gate. 
   
   
     6. An arc suppression circuit according to  claim 3 , further comprising a metal oxide varistor connected across the semi-conductor switch, whereby the power transistor is protected from overvoltage damage. 
   
   
     7. An arc suppression circuit according to  claim 3 , further comprising a diode connected in series with the semi-conductor switch and the battery-powered solenoid, whereby the power transistor is protected from reverse polarity damage. 
   
   
     8. A method for suppression of arcing across trip contacts used to turn off a battery-powered solenoid and trip an AC power circuit breaker, the method comprising:
 providing a semi-conductor switch connected across the contacts; 
 turning the switch on to provide a current path around the contacts before the contacts are opened; 
 holding the switch on while the contacts continue to open; 
 turning the switch off after a sufficient time has elapsed to prevent an arc from becoming established; 
 providing a capacitor connected to a resistance; 
 closing the trip contacts; 
 after closing the trip contacts, charging the capacitor; and 
 wherein the step of turning the switch on is performed a predetermined amount of time after the closing of the trip contacts; and 
 wherein the predetermined amount of time is determined by the capacitor and the resistance. 
 
   
   
     9. The method of  claim 8 , wherein the current path around the contacts carries substantially all of the current flowing through the battery-powered solenoid.